Machine tool vibration dampener



Dec. 10,1946. H. ERNST ErAL Y MACHINE TOOL VIBRTION DAMPENER Filed Aug. 30, 1944 i@ l I hlm.-

Patented Deal@ i946 Unirse STATES PATENT oil-Fics MACHINE TOOL VIBBATION DAMPENEB,

Hans Ernst, Daniel A. Grieb, and Michael Field, Cincinnati, Ohio, assigner! to The Cincinnati Milling Machine Co., Cincinnati, Ohio, a corporation ot Ohio Applicaties August so, 1944, sensi No. 551,912

11 claims icl. iso-11) invention should be readily apparent by rei'er-` ence to the following speciilcation, considered in conjunction with the accompanying drawing forming a part thereof and it is to be understoodv that any modifications may be made in the exact structural details there shown and described, within the scope of the appended claims.

Without departing from or exceeding the spirit oi.' the invention.

Referring to the drawing in which like refer-- f ence numerals indicate like or similar parts:

Figure 1 is a vertical longitudinal section through the overarm' and vibration damping mechanism comprising this invention.

Figure 2 is an lenlarged transverse section*A through the overarm and vibration damping mechanism on the line 2--2 of Figure 1.

Figure 3 is a fragmentary enlarged section of the front portion oftheoverarm on the line 3-3 of Figure 4. l v y Figure 4 is a fragmentary diagrammatic view of a.l portion of a typical milling machine to which this invention may be applied; s

In machine tools in which a relative movement of work and tool is provided for purposes oi' effecting a machining operation, vibration and chatter frequently are present due to the interaction ot cutter and work piece. Such vibration and chatter are particularly present in milling machines, especially of the horizontal type utilizing an overarm to provide the out-- board support i'or the cutter arbor driven from the cutter spindle of the machine. In such a milling machine structure the intermittent inter-action between cutter and work due to the successive presentation oi the cutting edges of the milling cutter to the work niece during the feeding movement frequently resultsv in inaccuracies and chatter marks in the finished work surface and damage to the cutter and the power transmission of the machine if vallowed to con tinue unrestricted.

It is recognized that ,in such a milling machine the outer end portion of the overarm, removed from the column portion to which the overarm is clamped to the machine frame, particularly partakes of violent vibration, especialb in instances where the outer end of the overarm cannot be appropriately held to the machine frame by a suitable brace. In such instances the outer portion of the overarm lmay oscillate rapidly under heavy cutting operations to such an extent as to make such machining operations unsatisfactory. It*is.therefore, the purpose 'of this invention to provide a vibration damping mechanism incorporated in the overarm which is automatically effective at any time to minimize or reduce vibrationin the overarm structurewhen utilized as an outboard support for the cutter arbor so that the machine may ree :'.fly be utilizedv for high production work under these conditions without giving rise to oby jectionable chatter and vibration..

' For illustrative purposes, this invention. is shown applied to a typical horizontal type of milling machine, Flgured, having the 'usual column .l 0 on which is appropriately mounted the worktableli and upon which may be placed the work W. 'I'he table H may feed the work W in the direction of the arrow i2 to a suitable milling cutter i3 to effect the desired machining operation. The milling cutter i3 is carried onl a suitable arbor i4 which is mounted at its rear end in the usual cutter spindle (not shown) lof the milling machine carried in the column I0 and driven by any conventional transmission mechanism. The outer end of the arbor is supported by means ot a suitable arbor support i5 depending from the housing or overarmil by -me'ans of suitable guideways Il and I8 formed on the underside o! the overarm. The overann is mounted for appropriate alignment of the arbor support I! with the arbor Il and cutter spindle by providing suitable dovetail guideway surfaces I9 and 20 in the top portion of the column lo which .may be rigidly clamped by any suitable clamping means lla to the guideways lil and I8 oi the overarm to securely hold its rearward portion lla to the machine column i or frame.

It can be seen that the rear portion Ita of the overarm isthus positively held against vibration on the machine column i0. However, the frontward projecting .portion iSb extending out beyond the column and carrying the overarm support i5 is unsupported and may be deflected transversely, as indicated by the arrow Ila, Figure 4, in vibxatory oscillating motions perpendicular to the types of machining operations due both to the number and pitch of the teeth of the cutter, the rate of rotation of the cutter, and the character of the material being machined. Because of this 'great variation in the frequency of vibration it is necessary to provide some means for absorbing and minimizing the vibration in the overarm which has a wide range of effectiveness.

In order to accomplish this, there is provided a vibration damping mechanism incorporated in the overarm comprising a mounting tube 2| which is rigidly clamped in bores 22 and 23 by appropriate clamping screws 24 threaded in clamps 25 which engage at the points 26 the inside bore of the tube 2l so as to rigidly hold this tube in the bores. It will be noted that the bores 22 and 23 are positioned in the overarm at its rearward portion within the confines of the area where it is normally clamped to the column I of the machine when in its extended outward position from the machine column asshown in Figure 1. Thus. the portion of the tube 2la between the bores 22 and 23 of the overarm is rigidly held against any movement relative to the overarm and the machine frame.

'I'he mounting tube 2| has a portion 2lb which projects outwardly toward the front of the machine from the mounting bore 23 in the overarm and is unsupported at its outer end so that it is resilient and free to permit its outer end to have transverse vibratory movements whenV acted upon by forces created during the machining operation, There is provided a suitable inertia member or weight 24 which may be actuated in tuned frequencies with the frequencies of vibration of the overarm. This weight is appropriately rigidly attached to the outer unsupported end of the mounting tube I2| and oscillates back and forth with the resilient portion 2lb of 4the mounting tube. Thus, the entire mass of the weight 24 is supported through the resilient portion 2lb of the mounting tube 2l in the rigid supporting boresv 22 and 23 formed in the overarm i6.

In order to effect a vibration damping action between the weight 24 and the outer vibrating end l6b of the overarm I6 there'is provided a frictional interengaging or damping means therebetween whereby vibratory oscillations in the outer end of the overarm sets up compensating out-ofphase vibratory oscillations in the Weight 24 which tends to neutralize and minimize the amplitude of vibration initially created in the overarm by action of the cutter and work piece during the machining operation. This frictional interconnection comprises, Figure 3, a guide sleeve 25 rigidly fixed to the mounting tube and counterweight 24 by screws 25a. and pin 25h. This sleeve is provided with a bore 26 in which is accurately slidably mounted a pressure spool 21 having anenlarged outer end to which is fixed a friction disc 28 which engages a friction surface 29 formed on a'suitable friction plate 30 rigidly mounted onthe overarm i6 by suitable screws 3l Means are provided for maintaining a predetermined amount of pressure longitudinally of the mounting tube and overarm by pressure between the composition friction disc 23 and the friction surface 29 of the plate 30. A compression sprintf` 32 is provided which abuts against a suitable washer 33 bearing against the surface 34 of the weight 24 and which is conned at its other end by anabutment spool 35. This spool may be moved axially to change the degree of compression of the spring 32 by a suitable adjusting be adjusted to increase or decrease the compression in the spring 32 which normally forces the pressure spool 21 outwardly longitudinally of the mounting tube 2l to cause the friction disc ,to engage the transverse friction surface 29. It is to be noted that the friction surface 29 is parallel to the direction of transverse oscillating vibrating movement of the overarm. By varying the degree of pressure exerted by the spring 32 the frictional coeiiicient of relative movement between the weight 24 and the overarm I6 may be adjusted to any desired value. A suitable locking set screw 38 is also preferably provided in the threaded bore 31 to rigidly hold the set screw 36 in adjusted positions. A closure screw 39 may also be provided in the friction disc 30 which may be readily removed when making adjustments in the set screw 36.

In operation as the cutter I3 engages the work W causing vibration to be set up in the overarm I6, the frictional interengaging means between the friction disc 28 and plate 30 will tend to likewise cause the weight 24 to vibrate. However, because of the slipping action between the composition disc 28 and the surface 29 there will develop a lag or out-of-phase relationship between the oscillatory motions of the overarm and the inertia member. The mounting tube and inertia member are so proportioned as to have a natural frequency of vibration substantially the same as the natural frequency of vibration of the overarm so that by appropriately adjusting the set screw 36 and thereby the frictional coefficient between the composition disc 28 and the friction surface 29 the lag or out-of-phase relationship may be tuned so that the weight 24 will be normally oscillating in the opposite direction relative to the oscillation of the overarm I'o`. In this way, the energy created through the frictional engagement of the disc '28 will tend to neutralize the vibration set up in the overarm `by the lcutting action. Thus, the vibration damping mechanism incorporated in the milling machine overarm may be readily tuned and adjusted to absorb vibratory movements set up in the overarm by the cutting action of Work and tool.

An improved feature of this arrangement lies in the-fact that this overarm vibration dampener is effective at relatively low frequencies of vibra tion of the overarm. This is due to the fact that the weight 24 is carried solely by the resilient mounting means or tube 2l on the non-vibrating portion I6a of the overarm which is rigidly clamped to the machine frame. Thus, under conditions of low frequency vibration the resiliency of the mounting means is so arranged that the weight is not carried along by the low frequency vibration in the overarm but tends to remain in a fixed rigid position -to thereby oppose low frequencies of Vibration set up in the overarm by direct frictional opposition through the disc 28 and the surface 29. Under these conditions the vibration damping mechanism serves, as an addition supplementary member to give added rigidity to the overarm.

There has therefore been provided a vibration v damping mechanism for an overarm which is in the pressure spool 21 so that the set screw may readily effective through a complete range of high. and low frequencies of vibration to damp out.

vibration and furnish added rigidity to the overarm structure during the machining operation. What is claimed is: 1. In a machine tool structure comprising a main frame, a. work support on said frame, a tool support onsaid frame movable relative to said work support for interaction of work and tool in said machine, and vibration damping means associated with said tool support including an inertia member, resilient means mounted on said frame providing the sole means for supporting said inertia member, and frictional interengaging means between said inertia member and said tool support to restrict relative vibrational movements ibetween the inertia member and tool support.

2. In a machine tool structure comprising, a frame, a tool support, and means for limiting vibrational movements in said tool support relative to said frame comprising a vibration damping mechanism including an inertia member, resilient means connected to said frame providing the sole means for supporting said inertia member, and frictional interengaging means between said inertia member and said tool support to limit relative vibrational movements of said tool support and said frame.

3. In a machine structure having, a main frame, a work support on said frame, a tool support on said frame, an outboard supporting means for said tool support mounted on said frame, and vibration damping mechanism to limit vibratory motion in said outboard supporting means including the combination of a weight, means mounted on said outboard supporting means at the point of its connection with said machine frame providing the sole means for resiliently supporting said weight, and frictional interengaging means between said weight and said outboard support to damp vibratory motion in said outboard support.

4. In a machine tool organization comprising a frame. a work support on said frame, a tool support on said frame, a supplemental support for said tool support mounted on said frame. and vibration controlling mechanism, for said supplemental support including a resilient mounting means xed to the said frame, a vibration damping weight mounted on said resilient mounting means, and frictions] interengaging means between said weight and said supplemental supporting means to damp vibrational movements in said supplemental support.

y5. In a milling machine having a column, a work support, and a cutter movable relative thereto, an overarm fixed on said column, an outboard support on :aid overarm for supporting said cutter, and vibration damping mechanism associated with said overarm including an inertia member, a resilient mounting means for said inertia member, comprising a ilexible tubular member rigidly connected to said overarm substantially at the point of clamping of said overarm to said column, and frictional interconnecting means between said inertia member and the outer end of said overarm to damp out relative vibrational movements therein during the cutting operation oi the machine.

6. In an overarm structure for a milling4 machine comprising an elongated hollow housing,

means for clamping one end of said housing Ato.

the column of the milling machine, means-.sproviding an outboard bearing support at the other end of said housing, a resilient tubular member fixed to said housing at the point of clamping of said housing to the milling Imachine column, a vibration absorbing inertia member xed to the outer end of said tubular supporting member, and

frictienai mterengaeins means between sai-d inertia member and said housing.

'1. In an overarm structure for a milling machine comprising a rectangular elongated hous- -5 ing. means for clamping one end of said housing to the column of the milling machine, means providing an outboard bearing support at the other end lof said housing, a resilient tubular member iixed to said housing at the point of clamping of said housing to the milling machine column, a vibration absorbing weight xed to the outer end of said tubular supporting member,

frictional damping means between said weight and said housing, andmeans for adjusting the i'rictional damping means to-vary the e'ective frequency of vibration damping.

8. In a milling machine having a column, a work support mounted, on said column, a horizontally extending overarm clamped at one end to said column, a cutter spindle in said column, vs. cutter arbor including a cutter mounted in said spindle, an arbor support depending from the outer end of said overarm and supporting said arbor, and vibration damping mechanism in said overarm comprising a resilient tubular mounting member extending longitudinally of said overarm and rigidly xed to said overarm at the end thereof clamped to said column, a weight fixed on the outer free end of said resilient tubular mounting member, and an adjustable frictional damping means between said weight and the outer unclamped end of said overarm adjacent said arbor support to damp out vibrational movements in said overarm and arbor support.

9. In a Vibration damping mechanism for a milling machine overarm comprising a hollow longitudinally extending body portion adapted to be clamped at one end to a rigid portion of the milling machine structure and adapted at its other end to carry an outboard support for a cutting tool of the machine, a vibration damping weight resiliently attached to said overarm at the point of clamping of said overarm to said machine structure and located adjacent the other x5 end thereof, and frictional damping means between said weight and said overarm, and means for effecting a variation in the frictional characteristics of said damping means.

10. In a milling machine structure including 50 a frame and an overarm adapted to have one end portion clamped to said frame, the combination of an inertia member resiliently supported from the clamped portion of said overarm in a position adjacent the free end thereof and frictional 55 damping means between said overarm and said inertia member to transfer vibration from said overarm to said member.

11. In a milling machine having a column and an overarm adapted to be clamped at one end to 60. said column, a vibration dampener for said overarm including an inertia member, means for supporting said member from the end of said overarm clamped to the column, a frictional damping means between said member. and the outer 65 end of said overarm to cause said member to vibrate in opposed oscillatory motion during high frequency vibration of said overarm and to act as a rigid member to oppose low frequency vibration in said overarm by direct frictional opposi- 70 tion through said damping means.

i HANS ERNST.

DANIEL A. GRIEB. MCHAEL -FIELD. 4 

